<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<canvas id="canvas"></canvas>
<!-- 顶点着色器 -->
<script id="vertexShader" type="x-shader/x-vertex">
    attribute vec3 a_Position;
    void main() {
        gl_Position = vec4(a_Position, 1.0);
        gl_PointSize = 100.0;
    }
</script>
<!-- 片元着色器 -->
<script id="fragmentShader" type="x-shader/x-fragment">
    void main() {
        gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
    }
</script>
<script>
    // canvas 画布
    const canvas = document.getElementById('canvas');
    canvas.width=window.innerWidth;
    canvas.height=window.innerHeight;
    // webgl画笔
    const gl = canvas.getContext('webgl');
    // 顶点着色器
    const vsSource = document.getElementById('vertexShader').innerText;
    // 片元着色器
    const fsSource = document.getElementById('fragmentShader').innerText;
    // 初始化着色器
    initShaders(gl, vsSource, fsSource);
    const a_Position=gl.getAttribLocation(gl.program,'a_Position');
    gl.vertexAttrib3f(a_Position,0.5,0.5,0.0);
    // 指定将要用来清理绘图区的颜色
    gl.clearColor(0., 0.0, 0.0, 1.0);
    // 清理绘图区
    gl.clear(gl.COLOR_BUFFER_BIT);
    // 绘制顶点
    gl.drawArrays(gl.POINTS, 0, 1);

    function initShaders(gl,vsSource,fsSource){
        //创建程序对象
        const program = gl.createProgram();
        //建立着色对象
        const vertexShader = loadShader(gl, gl.VERTEX_SHADER, vsSource);
        const fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fsSource);
        //把顶点着色对象装进程序对象中
        gl.attachShader(program, vertexShader);
        //把片元着色对象装进程序对象中
        gl.attachShader(program, fragmentShader);
        //连接webgl上下文对象和程序对象
        gl.linkProgram(program);
        //启动程序对象
        gl.useProgram(program);
        //将程序对象挂到上下文对象上
        gl.program = program;
        return true;
    }

    function loadShader(gl, type, source) {
        //根据着色类型，建立着色器对象
        const shader = gl.createShader(type);
        //将着色器源文件传入着色器对象中
        gl.shaderSource(shader, source);
        //编译着色器对象
        gl.compileShader(shader);
        //返回着色器对象
        return shader;
    }
</script>
</body>
</html>
